For some of my clients a single column seems to suit better but for others a 2-column layout seems better, ie. one large column and one narrow column on the RH side, I call it a sidebar (is that correct?!).
As I see it, sidebar can be useful for "hotspots" such as special offers and downloads.
Where they're less useful is...
...they take up space
...can cause the layout to be too complex, bad user experience.
...and of course when converting to plain text the sidebar plain text appears below the text from the main column.
What are the views of everyone else? Single column or 2-column? Which is better and why?
Is there any statistical hard evidence to back this up?
Good question, Julian.
I don't recall seeing any research on this. Does anybody have MarketingSherpa's Email Marketing Benchmark Guide?
I think it really depends on the message you're sending.
I wouldn't use if I was trying to get a single message across, like in a typical announcement leading to a single action.
I also don't think I'd use it for an email with a lot of copy. There's always the risk that the sidebar will divert attention from the main content.
It obviously depends on the content of the sidebar and the overall design too.
Like you, I think it can be useful for secondary content, but the only way to know for sure, is to test it.